In arrangements for high density recording on recording disks such as high speed magnetic digital recording for computers, workers are well aware of the difficulty in positioning read/write transducers e.g., in following or centering on a given track once the track has initially been located. For instance, such problems are particularly severe in present day magnetic recording on a stack of disks where at least a portion of a disk face is allocated to servo data [servo tracks]. One common approach is to key upon data signals from a given servo track [e.g., track 1 referencing upon band signals from band one and band zero of the associated servo track]. A vexing problem is knowing when one is really "on-center"--at times defined as being within x inches of the exact radial track center (cylinder). This invention addresses this problem, for instance, reporting when a servo transducer is truly "on-center" and also "off-center"--"on-center" being defined, for instance, as being within a "window" of .+-.50 uin of the exact cylinder center.
Conventionally, workers have attempted to find track center and to "follow" it by generating and monitoring "position" and "position quadrature" signals derived from the servo head positioning signal [reading-off a selected servo track]. One big problem with this approach is that the conventional techniques have been susceptible to frustration because of "noise", such as the commonly-observed noise spikes from a servo track [e.g., caused by a scratch or asperity or like anomaly on the servo recording surface] or noise from the transducer or its associated circuitry. For example, workers have attempted to simply hi-frequency filter-out such signals with a lo-pass filter. Such filtration, however, is quite imperfect; for instance, characteristically causing a delayed feedback of the "true center" signal and other problems. The invention addresses this problem and provides a Fine-positioning arrangement especially apt for track-following, one that is immune from typical noise. The invention additionally, preferably, uses means that also report when one is within .+-.x uin. of "true" track-center. For instance, the invention, in its preferred form, focuses on x=50 uin and additionally can focus on a second "marker", closer to track center, for instance, at .+-.30 uin. from track-center.
Thus, it is an object hereof to address at least some of these problems and provide at least some of the mentioned features and advantages. Another object is to provide a Fine-positioning system for a disk drive.